622 
BULLETIN OF THE BUREAU OF FISHERIES 
gulls, which are poor divers, to get the scallops. Furthermore these gulls, notable 
scavengers, are abundant principally about harbors. 
Ducks, and possibly other water birds, occasionally feed extensively on young 
scallops. In the winter of 1921-22 the white-winged scoter was found to be decidedly 
destructive to scallops in Massachusetts (Nelson, 1922). 
The oyster drill, listed by Belding (1910) as a principal enemy of the scallop, 
does not seem to be destructive here, for almost no drilled scallop shells have been 
noticed. It is thought that ordinarily the drill, which moves slowly, is not an impor- 
tant enemy of the scallop, which is active and quick moving. 
The starfish is considered by Uexkiill (1912) to be the principal enemy. Possibly 
it is, except for man, the principal predatory enemy of adult and juvenile scallops. 
Locally, starfish occasionally are found eating scallops. Of the recently emptied 
scallop shells generally to be found on scallop beds, it is impossible to say what portion 
are the work of the starfish, for, unlike the drill, it leaves no identifying mark. It 
has not been found in great abundance on North Carolina scallop grounds. In some 
regions the starfish may be extremely destructive. In North Carolina it probably is 
considerably destructive but not a menace. The experiments of Dakin (1910) and 
Uexkiill (1912) indicate that the scallop particularly avoids starfish. 
Possibly predatory planktonic forms and larger animals which feed upon plankton 
are much more destructive of scallops (larvae) than any forms which prey upon 
juveniles or adults. 
As previously noted, examination of tables and graphs of scallop collections, 
shows tremendous reduction in abundance of scallops above the smallest sizes. (See 
Tables 4 and 7 and figs. 23 and 24.) During times of abundance the largest collec- 
tions of scallops under 5 millimeters is about eight times as great as that of any 
group over 5 millimeters at any time of the year. Moreover the smaller sizes are 
much more apt to escape notice than larger ones. Thus an average mortality of 
perhaps 85 per cent between some size under 5 millimeters and one between 5 and 
10 millimeters is indicated. More specifically, from Table 9, it appears that mor- 
tality is most severe from 3.5 to 10 millimeters. There is no evidence as to whether 
or not this is due to predatory animals. 
Comparatively few scallop parasites seem to be known. Dakin (1909) found 
Lichomolgus maximus, an ectoparasitic copepod, on the gills and mantle of Pecten 
maximus, but no internal parasites in that species or in P. opercularis. At Beaufort 
I have found trematodes and a nematode. 
According to the investigation of Dr. N. A. Cobb (1930) only one nematode 
(a larva) previously has been found in a scallop (Yadel, 1855). The one ( Paranisakis 
pedinis Cobb, 1930) I found in the visceral mass thus appears to be the second ever 
found in a scallop. 
It has been reported (private correspondence) that trematodes are not found in 
P. irradians at Woods Hole. At Beaufort I have found them on the gills, in the 
gills, and in the walls of the stomach. 
On a few occasions I have found scallops the gills of which bore large numbers 
of trematode sporocysts. When these were examined fresh, each sporocyst was found 
to contain several redise and each redia hundreds of cercarise which were released 
when a cover glass was placed over a redia (so that the cercarise were released pre- 
maturely and may have differed considerably from mature cercarise). Some few 
cercarise were surrounded by a membrane, presumably the original covering of the 
germ ball. 
